Field of the Invention
The present invention relates to a vibration type actuator apparatus that is increased in position detection accuracy, a controller that controls the driving of an actuator of the vibration type actuator apparatus, and a medical system equipped with the vibration type actuator apparatus.
Description of the Related Art
As an example of an actuator that generates a driving force, there has been known a vibration actuator that brings a vibration element and a driven element into pressure contact with each other, and excites a vibration in the vibration element by applying an AC signal to thereby move the vibration element and the driven element relative to each other. The position control technique using the vibration actuator is used in various fields, such as an auto focus mechanism of an image pickup apparatus, a robot, a conveying equipment, a printing apparatus, and various manufacturing apparatuses. Of these various uses, the use in a field requiring particularly precise position control makes it necessary to increase the position accuracy during the driving and stopping of the vibration actuator. To meet this requirement, a measure is taken against electromagnetic noise, mechanical vibration, etc., which lowers the position accuracy.
The technique for coping with electromagnetic noise and mechanical vibration is roughly classified into one for preventing electromagnetic noise and mechanical vibration from entering the apparatus, and one for minimizing the influence of electromagnetic noise or mechanical vibration having entered the apparatus. Examples of the former technique include a technique related to e.g. an electromagnetic shield and a mechanical damper. This technique makes it possible to prevent electromagnetic noise and mechanical vibration from entering the apparatus, and hence provides a very large advantageous effect. However, the installation of an electromagnetic shield or a mechanical damper in the apparatus has a demerit in that the volume and weight of the apparatus are increased. On the other hand, examples of the latter technique include one related to a filter circuit inserted in an electric circuit, which can provide a certain effect while suppressing an increase in the volume and weight of the apparatus. However, a filter circuit having high noise elimination performance has a demerit in that delay in the temporal phase of the signal is increased, which degrades the stability and quick responsiveness in position control characteristics. In view of these problems, as a matter of fact, the former technique and the latter technique are often carried out in combination.
The latter technique also includes an example which suppresses noise superimposed on a position detection signal used in the actuator apparatus using an actuator. For example, Japanese Patent Laid-Open Publication No. 2012-186897 discloses a technique used in a controller for a pulse motor, for eliminating noise superimposed on a detection signal output from a position sensor connected to the pulse motor, using a filter. Further, Japanese Patent Laid-Open Publication No. 2001-241971 discloses a controller using a high pass filter for changing a cut-off frequency according to a rotational speed so as to extract a position detection signal from a ripple current of a DC motor. Furthermore, Japanese Patent Laid-Open Publication No. 2000-270575 discloses a low-pass filter used in a controller for a vibration actuator, which is capable of changing a cut-off frequency according to an amount of chattering of an encoder signal (position detection signal).
However, the technique described in Japanese Patent Laid-Open Publication No. 2012-186897 uses the filter that is capable of changing a cut-off frequency based on a speed command, and sets the cut-off frequency of the filter in proportion to the speed command. This cause a problem that the cut-off frequency of the filter during the stop of the pulse motor is mathematically equal to 0 (zero) Hz, and as a result, it is impossible to sufficiently detect changes in a position signal during the stop of the pulse motor. Further, since the cut-off frequency is set in proportion to the driving speed of the pulse motor, a phase delay in the position signal detected when the pulse motor is controlled to a low speed is relatively larger than a phase delay in the position signal detected when the pulse motor is controlled to a high speed, which lowers the stability and quick responsiveness when the pulse motor is controlled to a low speed.
In the technique disclosed in Japanese Patent Laid-Open Publication No. 2001-241971, since the high pass filter is used, as the rotational speed of the DC motor becomes lower, the amplitude of the position signal after being subjected to filtering is reduced, and when the motor is stopped, the signal ceases to be output. This causes a problem that the position detection accuracy is lowered when the motor is stopped.
The technique disclosed in Japanese Patent Laid-Open Publication No. 2000-270575 has a problem that the cut-off frequency of the low-pass filter is adjusted after noise is detected, and hence it is impossible to cope with sudden noise. Further, the cut-off frequency is not changed according to the driving speed of the vibration actuator, and hence it is impossible to perform control in quick adaptation to differences in vibration characteristics and control characteristics of the vibration actuator between when stopping the vibration actuator and when driving the vibration actuator.